1. Field of the Invention
The present invention relates to a method and apparatus for writing images using ink and, particularly, to a writing method for an ink jet printer using electro-rheological fluid and apparatus thereof which controls the ejection of ink by using an electrical potential for varying the viscosity of the fluid and a pressure difference of a venturi tube.
2. Description of the Background Art
Electro-rheological fluid is well-known for its electro-field responsiveness. The electro-rheological fluid was first disclosed in U.S. Pat. No. 2,417,850 by Winslow in 1943, and has been proposed in various forms in U.S. Pat. No. 3,047,057 by Winslow, USSR patent 1391951 by Lysenkov and U.S. Pat. No. 4,812,251 by Stangroom.
Such electro-rheological fluids proposed by the aforementioned publications are basically made of electric-viscosity liquid containing a powdery additive of a minute particle diameter which, if an electric field is applied thereto, become varied in the viscosity. Here, viscosity has been known to vary proportional to the strength of the applied electric field, which is referred to as electric viscosity effect. The electric viscosity effect is that the viscosity of a fluid is varied depending on the strength of an applied electric field, and varies almost concurrently with the electric field application. Among the above-described electro-rheological fluids, there is one whose viscosity varies from a liquid state to a nearly solid state even by an electric field below 10 KV/mm.
Utilizing ink made with electro-rheological fluid and an appropriate controller, written images can be created. Technology for writing images using such electro-rheological ink has been disclosed (IS&T conference 91' 11).
A conventional head for ejecting such electro-rheological ink is illustrated in FIG. 1 which utilizes a nozzle sheet 1 and a pair of support sheets 2 and 3 that are stacked above and below the nozzle sheet respectively. Nozzle sheet 1 has an ink reservoir 1a for receiving ink of a certain quantity and a nozzle 1b for ejecting ink therefrom. Upper support sheet 2 has an ink supplying aperture 2a and an electrode plate 4, and lower support sheet 3 has another electrode plate 4'. In this configuration, a predetermined pressure is kept with respect to the inside and outside of nozzle 1b. The viscosity of the ink inside the nozzle is varied according to a writing potential, illustrated schematically at reference numeral 5, applied to a pair of electrode plates 4 and 4'. When the ink has a low viscosity, i.e. liquid, the ink is ejected due to the pressure difference between the inside and outside of the nozzle. That is, the viscosity of the ink inside the nozzle is varied by the strength of the electric field formed by the two electrodes, so that the ink is ejected when it has a high viscosity, i.e. nearly solid, and is not ejected when the ink has a low viscosity. Such a technology for ejecting electro-rheological ink according to the writing potential requires an additional means for creating the pressure difference inside and outside the nozzle and holding the pressure difference. This causes the apparatus to be complicated and expensive while impeding its miniaturization.